It is known that 2-alkenals corresponding to the general formula H.sub.2 C.dbd.CR--CHO wherein R is hydrogen or alkyl, such as, for example, acrolein or methacrolein, can be hydrated to the is corresponding 3-hydroxyalkanals in homogeneous phase with water in the presence of acid catalysts (U.S. Pat. No. 2,434,110). 3-Hydroxypropionaldehyde can be prepared from acrolein in this way. 3-Hydroxypropionaldehyde can be further processed by means of hydrogenation to form 1,3-propanediol, which is gaining increasing importance as a monomeric structural unit for polyesters and polyurethanes. The process described in the document U.S. Pat. No. 2,434,110 has the disadvantage that only a low yield and a low selectivity can be achieved.
The use of carbon dioxide as catalyst is known from the document GB-A 1185615. Because of the very long reaction time, however, only very low space-time yields can be achieved.
A process for the hydration of 2-alkenals in a homogeneous medium, in which an acid-base buffer is used as catalyst, is known from the document EP-B 0 544 118. However, the known process has the disadvantage that the space-time yield obtained is not sufficient.
The documents U.S. Pat. No. 3,536,763 and DE-A 3,926,136 disclose processes for the hydration of 2-alkenals wherein heterogeneous catalysts, such as for example ion-exchange resins, are used. But the disadvantage of these processes is that they require a filtration step during the working up of the reaction mixture.